In the first study
to rigorously track the movements of preschoolers, scientists
found that the average 3-year-old is physically active for just
20 minutes a day, well short of the recommended hour a day for
that age.

In The Lancet study
published this month, scientists from the University of Glasgow
in Scotland recruited 78 children. Each 3-year-old wore an "accelerometer,"
a matchbox-sized monitor clipped to the waistband, for a week.

The device, worn
from the time the children woke up until they went to bed, gave
minute-by-minute readings of the children's pattern of physical
activity and the number of calories burned.

The toddlers were
burning about 1,300 calories a day  less than the 1,500
calories recommended.

While the problem
is one of an imbalance of calories eaten and burned up, experts
believe the main reason is that children are not getting enough
exercise.

"There are really
only two possibilities, reduced activity or increased intake.
None of the dietary assessment data indicate that children are
eating more. Adolescents may be eating more but young children
are eating less," said the study's leader, John Reilly, a physiologist
at the University of Glasgow.

"A 3-year-old 25
years ago was eating 25 percent more than a 3-year-old today,"
he said. "But physical activity levels have dropped quite dramatically
over the last 15 or 20 years."

In the study, the
children were spending between nine and 10 hours of their waking
day hardly moving at all.

"They may well have
been doing a bit of fidgeting, they may have been speaking to
their parents or among themselves, but they were just not moving
enough to put up the number of calories burned beyond what it
would be if they were just resting or sleeping," Reilly said.

The children spent
20 minutes a day in moderate to vigorous activity  the
type of activity that would get them feeling slightly warm and
slightly out of breath, such as running around, walking to keep
up with an adult and most types of outdoor play.

All-day television
and recorded videos are a major culprit, Reilly said. Outside
the home, children are also much less active than they used
to be.

"Many more journeys
are made by car and among the 3-year-olds, a fair number of
them are being taken around in strollers when they could arguably
have been walking," Reilly said.

Another element
is recent concerns over safety. Some local authorities in Britain
have banned children from bringing balls into playgrounds while
others prohibit tree-climbing.

"There needs to
be a balance. Perhaps we've taken the health and safety agenda
a bit far," Reilly said.

The dangers of a
sedentary childhood go beyond obesity, experts said. More active
children tend to be better behaved and scientists suspect that
more active children learn more effectively, perhaps because
physical activity is a stimulus to brain development.

"The increasingly
sedentary nature of U.K. children is not unique and is being
seen in most countries around the world," said James Hill of
the Center for Human Nutrition at the University of Colorado.

Small changes in
behavior are all that is needed, said Hill, who was not connected
with the study.

In the days before
videos and TV, young children didn't sit for hours staring at
the wall, Reilly said. "They were perfectly capable of finding
other ways to amuse themselves. They had imaginations. They
still have imaginations," he said.